The present invention relates to the regeneration of elemental halogens from hydrogen halides and/or hydrohalic acids and more specifically to the use of a molten salt to catalytically oxidize hydrogen chloride to produce chlorine in the absence of an oxygen-bearing gas.
In the production of organic chlorides for use in plastics and other products, large amounts of hydrochloric acid are frequently produced as a by-product or waste. This excess hydrochloric acid is traditionally either utilized productively, if possible, or neutralized with limestone and discharged to the environment as an aqueous waste. Due to the increasing restrictions on the discharge of pollutants and the rising cost of chlorine, it has become more attractive to provide a method for regenerating chlorine from the by-product hydrochloric acid. Previous methods for regenerating chlorine from hydrochloric acid have, however, met with engineering and economic problems which prevented their implementation on a large scale.
It is presently known that hydrogen chloride, for example, may be oxidized with sulfur trioxide to produce a mixture of chlorine and sulfur dioxide. This process requires a series of at least three separate process steps to obtain the mixture from which the chlorine must be subsequently separated.
Another prior method is the oxidation of hydrochloric acid with sulfur dioxide and oxygen in the presence of a bed of metal oxide catalysts to produce sulfuric acid and chlorine. The solid supported catalysts used in such systems are difficult to prepare and tend to deactivate or degrade rapidly.
Oxygen is also being used to oxidize hydrogen chloride in the presence of an oxide of nitrogen catalyst and an excess of sulfuric acid having a concentration of at least 65 percent. This process is complicated and expensive because it requires numerous process steps.
Hydrochloric acid has also been oxidized with oxygen in molten inorganic chlorides and an olefin chlorine acceptor such as ethylene. Such systems must accomodate complex chemical reactions which produce a variety of different reaction products. Also, because inorganic chlorides tend to volatilize in the reaction zone, the catalyst is driven off and separation of chlorine from the reactor effluent is difficult. Furthermore, operation with chloride salts is corrosive to process equipment.
In addition, hydrochloric acid has been regenerated by means of electrolytic processes which are expensive and which require substantial electrical energy consumption.